This is a proposal to study mitosis by elucidating the structure and function of kinetochores, centrioles, and microtubules. The principal method of approach will employ laser microbeam irradiation followed by electron microscopy or cell cloning. The kinetochore studies should clarify (1) the molecular (DNA and protein) organization within this structure, (2) the ability of the kinetochore to replicate and repair itself, (3) the role of the kinetochore in chromosome movements. The centriole studies will elucidate (1) the molecular organization within this organelle, (2) the role of the centriole replication in the cell division process, and (3) the role of the centriole and pericentriolar region in mitotic spindle organization and maintenance. Studies will also be undertaken (1) to determine the role of the centriole in the organization of kinetochore and continuous microtubules, (2) to elucidate the mechanism of the centriole migration, and (3) to elucidate the biophysical nature of laser light interaction with biological systems.